Integrated circuit (IC) technologies are constantly being improved. Such improvements frequently involve scaling down device geometries to achieve lower fabrication costs, higher device integration density, higher speeds, and better performance. Along with the advantages realized from reducing geometry size, improvements are being made directly to the IC devices. One such IC device is an image sensor device. An image sensor device includes a pixel array (or grid) for detecting light and recording an intensity (brightness) of the detected light. The pixel array responds to the light by accumulating a charge—the more light, the higher the charge. The charge can then be used (for example, by other circuitry) to provide a color and brightness that can be used for a suitable application, such as a digital camera. Common types of pixel grids include a charge-coupled device (CCD) image sensor or complimentary metal-oxide-semiconductor (CMOS) image sensor device.
One type of image sensor device is a backside illuminated (BSI) image sensor device. BSI image sensor devices are used for sensing a volume of light projected towards a backside surface of a substrate (which supports the image sensor circuitry of the BSI image sensor device). The pixel grid is located at a front side of the substrate, and the substrate is thin enough so that light projected towards the backside of the substrate can reach the pixel grid. BSI image sensor devices provide a high fill factor and reduced destructive interference, as compared to front-side illuminated (FSI) image sensor devices. In general, BSI technology provides higher sensitivity, lower cross-talk, and comparable quantum efficiency as compared to FSI image sensor devices.
Due to device scaling, improvements to BSI technology are continually being made to further improve the BSI image sensor device's quantum efficiency. For example, an antireflective coating (ARC) layer is disposed over the backside surface of the substrate to improve transmittance of light wavelengths to the substrate, and thus, to the pixel grid for sensing light. Typical ARC layers include silicon oxynitride (SiON) and/or silicon nitride (SiN) (such as a ultraviolet silicon nitride (UVSN) layer) layers. As technology nodes continue to decrease, for example, to 65 nm technology nodes and below, these typical ARC layers are intrinsically limited to the quantum efficiency improvements they can provide. Accordingly, although existing BSI image sensor devices and methods of fabricating these BSI image sensor devices have been generally adequate for their intended purposes, as device scaling down continues, they have not been entirely satisfactory in all respects.